You might think there’s not a lot to know before buying a blade for a circular saw, table, or radial arm saw, but when you look into it, your choices can be intimidating. Once you know a few basic terms and what they mean, and a few things about blade materials, types of teeth, tooth count, and a few other technical tidbits, you should be fine.
Here are a few terms and considerations you need to know in choosing a blade:
Application – You need to know both what type of saw you’re going to use the blade on and what types of materials you’re going to be cutting. Different circular saws and materials require (or perform best) with blades optimized for that operation. There are general purpose blades that can handle different materials, but if you know you’re likely to only (or mainly) cut one type, get a blade optimized for that.
Number of Teeth – How many teeth in a blade determines its cutting action. More teeth means a smoother cut, fewer teeth means that the blade removes more material. Crosscut blades have more teeth and make smoother cuts across the grain of the material, rip blades have fewer teeth, are optimized to cut with the grain, and remove a lot more material.
Gullet – The gullet refers to the space between each tooth on the blade. A wider gullet produces a bigger chip of material cut.
Tooth Configuration – The shape of the blade teeth also determines its performance. Teeth are configured to optimize crosscutting, ripping, and working through certain materials, like laminates, MDF, etc. Some common tooth types include Flat Top (FT), optimized for ripping, Alternative Top Bevel (ATB), optimized for crosscutting, Combination Tooth (CT), which includes both tooth types and is designed for general purpose cutting.
Tooth Angle – The tooth (or hook) angle refers to the angle of the tooth in relation to the center line of the blade. Blades with “positive hook angle” means that the teeth lean forward to a set degree. “Negative hook angle” means that the teeth are angled back, opposite the direction of blade rotation. The higher the positive angle of the blade, the more aggressive the blade.
Here are a couple of excellent YouTube videos that will further explain most everything you need to know to confidently buy saw blades. These are followed by a bit more information on important blade characteristics.
Canadian Woodworking also has a good getting started article. Among other useful things, it includes some rules of thumb for selecting a table saw, mitre, or circular saw blades:
- Blades with more teeth yield a smoother cut. Blades with fewer teeth remove material faster, but tend to produce a rougher cut with more “tearout”. More teeth means you will need to use a slower feed rate.
- No matter what type of saw blade you use, you will likely wind up with residue on the saw blade. You’ll need to clean off this residue using pitch solvent. Otherwise, your saw blade will suffer from “blade drag” and can produce burn marks on the wood.
- Do not use a rip blade to cut plywood, melamine, or MDF. This will result in poor cut quality with excessive “tearout.” Use a crosscut blade, or even better, a good-quality triple-chip blade.
- Never use a rip blade in a mitre saw as this can be dangerous and will provide very poor-quality cuts. Use a cross-cut blade.
Spot good quality at a glance. The best blades don’t scrimp on carbide or steel. Designed for long life, their teeth can be resharpened many times. Economy blades almost always have thin, stamped steel plates. Expansion slots that end bluntly in open holes signal old technology and a noisy blade.
[Source: Popular Woodworking]
The two basic types of table saw blades are rip and crosscut blades. Rip blades have a smaller number of teeth and larger gullets, which means there’s more room to remove the shavings and dust. These blades are designed to cut along the grain of the material on the table, but although they cut faster, the resulting cuts are rougher.
If finer cuts are what you have set out to achieve, a crosscut blade is the better option. The resulting cut is much smoother, but because the teeth have less space for chip removal and because there are more teeth to cut through the wood, the feed rate is much slower.
If you need both speed and smooth finish, there are combination blades, which attempt to do both. Also, you may come across special cut blades. These are either designed to cut through certain materials like plywood, hardwood, metal, plastic, or even brick, or they are designed to make specialized cuts for the purpose of joint making. This includes sets of dado blades.
[Source: The Sharp Cut]
In general, a blade with more teeth makes a smoother cut but runs hotter. To avoid overheating, three to five teeth should be engaged during a rip cut (see photo, right). For crosscuts and sheet goods, five to seven teeth should do the work.
To maintain the correct engaged-tooth ratio, a blade with fewer teeth for cutting thick stock would be ideal. Another solution is to adjust the blade’s height (with the blade guard in place). Raising the blade higher reduces the number of teeth in the cut. It also increases the hook angle, which makes the blade more aggressive, so the cut’s quality decreases.
[Source: Popular Woodwoorking]
Kerf Width and Plate Thickness
The width of the “kerf” – the slot the blade cuts in the material – is another important consideration. Most obviously, the kerf width determines the amount of material that is expended in the cutting process. But kerf width isn’t just a matter of economics. The size of the kerf is determined in part by the thickness of the blade plate, and a solid, reliable blade plate is one of the features of a good blade.
Thin Kerf Blades A saw blade’s teeth, of course, have to make a wide enough cut to allow the blade plate to pass through the kerf. And for the blade to operate smoothly and make a true cut without a lot of scoring on the edge of the cut, the blade plate has to be substantial enough to absorb vibration and to handle the heat generated during the cut. For a full kerf saw blade, a kerf width of around 1/8′ is standard. But for so called “underpowered” saws — under 3 HP for a table saw — a full 1/8′ kerf has another effect: drawing too much power from the tool. If not enough power is delivered to the blade, the saw slows down causing excessive friction. The blade heats up and can become distorted or burn the cut surface.
Understanding Expansion Slots
Many blades have expansion slots to allow the blade to expand and contract slightly, without throwing the blade out of true. [Source: Canadian Woodworking]